Belt transmission device

ABSTRACT

Speed change box comprising several transmission assemblies of which each, corresponding to a unique and different transmission ratio, comprises a respective transmission belt which can be applied, to permit the transmission of force, by pressure of a fluid, to a drive pulley and a driven pulley, and means for selectively applying the pressure of the fluid to a transmission assembly corresponding to the chosen ratio.

United States Patent [1 1 Bertin Nov. 20, 1973 [54] BELT TRANSMISSIONDEVICE 1,151,837 8/1915 Tannewitz 74/217 R [76] Inventor: Jean HenBenin, l we Deleau 3,636,784 1/1972 Sanstrom 74/217 R 92Neuilly-sur-Seine, France Primary Examiner-Leonard H. Gerin [22] Flled:July 1972 Att0rneyA1fred W. Breiner [21] Appl. No.: 275,151

[57] ABSTRACT [30] Foreign Application Priority Data July 30 1971 France7128056 Speed change several "ansmsswn semblies of which each,corresponding to a unique 52 us. 01. 74/217 R 74/242.11 s and differenttransmissm a respec' 51 Int. Cl. Fl6h 9/64, F16h 7/12 i i which be 58Field 61 Search 74/217 R 242.11 s the transmssm by Pressure fluld' drivepulley and a driven pulley, and means for selec- [56] References Citedtively applying the pressure of the fluid to a transmis- UNITED STATESPATENTS slon assembly corresponding to the chosen ratio. 499,159 6/1893Crafts 74/217 R 25 Claims, 19 Drawing Figures PATENIEUNDVZO I973 v SHEET10F 5 PATENTEI] NOV 2 0 1973 SHEET 2 [1F 5 PATENTEDHOV20|975 3.772.927

' SHEET 30F 5 PATENTEDHUV20 I975 SHEET H 0F 5 SHEET 5 [IF 5 PATENTEUHUV20 1975 BELT TRANSMISSION DEVICE The invention relates to devicespermitting the transmission of rotary motion from a driving motion froma driving shaft to one or more driven shafts, possibly with severalpossible gear ratios. The invention further relates particularly but notexclusively to a motor vehicle gear box.

The applicant has already applied for the French Pat. No. 2,431,738describing a system of transmission by belt or band, in which thepressure of a fluid is used to augment the pressure of the said band onthe support surface, and consequently to increase the driving force ofthe band.

The applicant has found that the use of such belts, in a well suitedform, facilitated gear changes and that it was possible to avoid,practically completely, the undesirable energy losses by thetransmissions in normal service; in addition, thanks to the goodapplication of the belts on the drive surfaces, slippage, and as aconsequence the wear of belts of this type, are reduced.

The device according to the invention comprises several transmissionassemblies each comprising a belt associated with a drive pulley and adriven pulley, the belts being able to be applied selectively on theirrespective pulleys by fluid cushions which are established facing atleast one part of the contact surface of the pulleys and the belts.

According to an embodiment of the invention, the transmission device maycomprise several shafts, for example a driving shaft and several drivenshafts, each driven shaft being able to be coupled to the drive shaft bymeans of at least one assembly of pulleys and belts. The transmissionratio of the pulley/belt assemblies of each driven shaft can be the sameor different. In addition, each driven shaft may comprise severalpulley/- belt assemblies having different transmission ratios.

According to another embodiment of the invention, the transmissiondevice comprises several pulley/belt transmission assemblies of whicheach, corresponding to a unique and different transmission ratio,comprises a respective transmission belt able to be applied, to permitthe transmission of the force,.by the pressure of a fluid, onto a drivepulley and a driven pulley, and means for selective application of thepressure of the fluid to a transmission assembly corresponding to theratio chosen.

Preferably, according to the invention, means are provided for movingthose belts which are not going to be used away from their respectivepulleys, to maintain them disengaged. These means can be arranged forexample to establish a weak counter-pressure of fluid between thepulleys and the belts of the transmission assemblies which one wishes tomaintain disengaged. Advantageously, these means are permanently inaction, their action being counterbalanced by the pressure exerted bythe cushions which apply the belts onto their pulleys.

Finally, it should be mentioned that the arrangement according to theinvention is particularly well suited, as will be seen, to the making ofspeed change boxes comprising in all two shafts, that is a drive shaftand a driven shaft, reversing being obtained without any supplementaryintermediate shaft.

The description which follows, relating to the annexed drawings, givenas an example which is no way limiting, will permit a betterunderstanding of how the invention can be carried out, the particularswhich arise from both the drawings and the text forming, it is to beunderstood, part of the invention.

In these drawings:

FIG. 1 is a diagrammatic view of the assembly of an installationaccording to the invention;

FIG. 2 is a sectional view on a larger scale of the speed change box Aof FIG. 1;

FIG. 3 is a sectional view showing a transmission device. according tothe invention, in engaged position;

FIG. 4 is a sectional view along the line IVIV of FIG. 3; I

FIG. 5 is a variation of the embodiment of FIG. 3;

FIG. 6 is a sectional view along the line VI-VI of FIG. 5;

FIG. 7 is a variation of the embodiment of FIG. 5;

FIG. 8 is a sectional view along the line VIII--VIII of FIG. 7;

FIG. 9 is a view on a larger scale, partly cut away, showing thetransmission device according to the invention comprising means forreversing the movement of rotation of the driven shaft;

FIG. 10 is a perspective view showing a pulley with a serrated surface;

FIG. 11 is a perspective view on a larger scale showing a detail of thedevice which confines the cushions for applying the belts onto thepulleys;

FIG. 12 is a variation of the embodiment of FIG. 1 1, showing a pulleywith notches and serrations;

FIG. 13a is a sectional view of a transmission device according to theinvention, furnished with a roller tensioner in engaged position;

FIG. 13b is a view analogous to FIG. 13a, the transmission device beingin the disengaged position;

FIG. 14 is a detailed view showing a device permitting the adhesion ofthe belts to the pulleys to be increased;

FIG. 15 is a sectional view showing a pulley furnished with segments tolimit leakages;

, FIG. 15a is a sectional view taking along the line XVaXVa of FIG. 15;

FIG. 16 is a variation of the embodiment of FIG. 15;

FIG. 16a is a sectional view along the line XVla-XVIa of FIG. 16.

In FIG. 1 is seen an assembly of an installation according to theinvention, particularly applicable to motor vehicles. The motor M isprovided with a radiator R and with a transmission box A according tothe invention, with several speeds, which are selected by means of afluid distributor comprising a hand lever B. An appropriate element C,actuated by the motor M, furnishes oil under pressure'to the box of thecontrol lever, which directs this oil along a corresponding channel c or0,, 0,, 0 c according to whether the oil pressure in box A is to beapplied, according to the case, to actuate respectively reverse movementor the first, second, third or fourth speed. It is particularlyconvenient, but not obligatory, to use as the fluid serving to apply abelt onto its pulleys, the oil present at the bottom of the housing ofthe motor M and serving to lubricate the motor.

Thus in speed change box A (FIG. 2), transmission assemblies, eachcomprising two pulleys and one connecting belt, of the type which isapplied by fluid under pressure, replace the usual pairs of gear wheels.A clutch D, for example of the conventional centrifugal type, isinterposed between the shaft 7 of the motor and the drive shaft 6 of thebox, this latter driving the driven shaft 8 via the transmissionassemblies. The driven shaft 8 and the drive shaft 6 are,advantageously, parallel.

In the present case, four fixed speeds have been provided, 1, 2, 3, 4(this last being stepped up) and a reverse 5. This reverse motion can beobtained very simply by the use of two engaged gear transmissions and ajaw clutch 5a; it could also have been obtained using the sameconstitution of that of the other transmission assemblies, by crossingthe belt which then takes the form of a figure 8.

According to FIGS. 3 and 4, a transmission assembly according to theinvention comprises a flexible band 9, a belt for example, transmittingthe movement, in the direction of the arrow F, at a chosenmultiplication ratio, from a drive pulley to a driven pulley l 1,respectively integral with shafts 6 and 8. The belt 9 can be applied onthe pulleys l0 and 11 by fluid cushions (oil) under pressure 12a, and12b. The cushions 12a, 12b supplied by the duct connected to the circuit13 exert a pressure, termed engaging pressure, on the whole of thecontact surfaces between the pulleys and the belts.

The devices which confine the cushions 12 can comprise detent chambers53 limiting leakages, and are connected to fluid evacuation conduits 54.The cushions 12a and 12b are connected to the speed selector B, whichsupplies them from a conduit termed high pressure circuit."

In order to obtain minimal frictional forces when the belt should not bein contact with the pulleys l0 and l 1 (disengaged position), a layer offluid at a pressure lower than the pressure of the cushions 12a, anddelivered by a circuit which is termed the low pressure circuit, iscreated between the belt 9 and the pulleys 10 and l 1.

The fluid used to form these layers can be the same as that utilized toform the cushions 12, oil for example, but to limit the forces due tointernal shearing of the fluid it is advantageous to choose a fluid oflower viscosity such as air or any other gas.

The low pressure fluid feed is effected by the channels 14 (FIG. 4)which are formed in the shafts 6 and 8 of the pulleys l0 and 11; thelayer of fluid is distributed over the surface of the pulleys by radialchannels 15.

In the exampleshown, the channels 14 feed all the pulleys.

Because of the difference of pressure existing between the cushions 12,on the one hand, and the layers of fluid formed between the belts 9 andthe pulleys 10 and 11, on the other hand, the conduits 15 can bepermanently fed by the channels 14; thus the belts which are not appliedon to their pulleys by the high pressure cushions 12 are automaticallymaintained disengaged.

Other devices for disengaging the belts may be used, possibly incombination with the fluid layers formed by the channels 15. For examplethe enclosures confining the cushions 12 of the devices which are to bedisengaged can be connected to a source of fluid at a pressure lowerthan the ambient pressure. Or again, if the belts are constituted by orcomprise magnetisable parts they can be attracted by electromagnetsplaced within the cushions l2 and supplied with electric current when itis desired to disengage the belts. The control of these electromagnetscan be coupled to the control B of the fluid distributor of the highpressure circuit.

To avoid leakages of fluid from the high pressure circuit via the radialchannel 15 which are not masked by the hand 9, opposing (or reaction)cushions, advantageously fixed, 16a, 16b, can be provided facing thesurfaces of the pulleys not in contact with the belt 9. These cushionspermit the equilibration of a part of the application forces acting onthe two shafts of the pulleys which are common to differenttransmissions assemblies 1, 2, 3, 4 and 5.

A tensioner 17 with a fluid slide block 17a (supplied from the lowpressure circuit) is advantageously provided between the pulleys 10 and11, particularly to compensate possible lengthening and to compensatethe flapping of the belts 9.

FIGS. 5 and 6 show a variant embodiment of the invention according towhich the cushions l2'a and l2'b are provided with internal partitions40 which define elementary cushions separately supplied via calibratedorifices 41 connecting them to a chamber 42.

In this embodiment, the opposing cushions l6a and 16'b also subdividedby partitions 43, are separately fed from chambers 44 and 44.

These chambers are connected by a conduit 45 to a source of fluid underpressure constituted for example by the high pressure circuit. In thiscase, the feed of the chambers 44, 44 is effected conjointly with thatof chambers 42 of the cushions for application of the belts.

The fluid slide block 17 may be applied to the belts by a jack 46 whenit is supplied from the conduits 45. An opposing spring 47 may beprovided to move the slide block 17 away from the belt when the latteris disengaged. The slide block 17 may be permanently fed (low pressurecircuit) or be supplied conjointly with the belt application cushionsvia conduit 45 connected to the high pressure circuit.

When the counter-reaction cushions 16' of a transmission assembly arefed with fluid under pressure, they may serve to form fluid layersbetween the pulleys and the belts of. other transmissionassemblies whichare to be maintained disengaged. For this purpose, taking account of ajudicious distribution of losses of load, a part of the fluid passedalong the channel 45 into the cushions 16' is transmitted by the radialchannels 15 and the axial channel 14 to the axial channels 15 of thetransmission assemblies which are to be disengaged. In this case, thefeed of the axial channels 14 via the low pressure channel may beeliminated.

According to the variantof FIGS. 7 and 8, the cushions l2a, and 12bexert their pressure (on engagement) on only a part of the pulley/beltcontact surfaces, for example about a sixth of the circumference, so asto utilize to a maximum the effect of rolling. For this, the cushions 12are situated substantially on the line of the zone of engagement of thebelts and of their respective pulleys. Opposing cushions 16'a, l6b areprovided on the whole of the surfaces of the pulleys not in contact withthe belt 9.

This tensioner 17 may be integral with a box for recovery of leakages offluid, comprising an exit 18.

FIG. 9 illustrates a complete transmission assembly including also thereversing device 5. Gear wheels 19 and 20, which can also be seen onFIG. 2, and mounted respectively on the drive shaft 6 and the drivenshaft 8, permit the movement to be reversed from the sense F to thesense F. As may be seen in FIG. 9, the difierent multiplication ratiosfirst (loo-11a), second (lob-11b), third (l0c-llc), fourth (Nd-11d) maybe obtained by using belts 9 of the same length (but which can be ofdifferent widths), which is an advantage in relation to the classicalgear boxes where the modulus of the pinions is a limiting factor.

According to FIGS. l0, l2 and 14, the serrations (or holes of any shape)21 permit a better drive coefficient of the belt 9 on the pulleys to beobtained. The band or belt 9 is deformed elastically by the pressure ofthe cushions 12, producing pseudo-teeth which mesh with the hollows ofthe pulley.

The cheeks of the pulleys may be furnished with grooves 22 (FIG. 12)which cooperate with lateral extensions 48 of the confinement devicesfor the cushions 12 and 16 and limit the leakages of these cushions.

The cheeks of the pulleys may be smooth (FIG. 11), labyrinths beingformed on the lateral extensions 48 of the devices confining thecushions l2 and 16.

The lateral extensions 48 of the confinement devices may compriseconduits for the evacuation of leakages of fluid forming the cushions 12(see FIG. 11, these conduits not been shown in FIG. 12).

According to FIGS. 13a and 13b, the device according to the invention isprovided with a pulley tensioner 24 coupled to the high pressure and lowpressure circuits by a jack 25.

In the engaged position (FIG. 13a), the tensioner coupled to the highpressure circuit exerts its pressure on the belt 9, increasing therolling length of the latter on the pulleys l0 and 11, which diminishesthe losses in the transmission of the motion.

In the disengaged position (FIG. 13b), the tensioner is coupled to thelow pressure circuit and moves away from the belt 9.

The transmission assemblies according to the invention may comprisesegments for limiting the leakages of the cushions.

For example, there may be seen in FIGS. 15 and 15a a part of atransmission assembly of which the pulley 10 (or 11) comprises groovesformed on its surface or revolution and in which are mounted segments 51which cooperate with the internal face of the belt 9 and the devices forconfining the opposed cushions 16. These segments limit the leakages ofthe low pressure circuit.

The leakages of the high pressure circuit are limited by the segments 28which cooperate with the external face of the belts and are situatedsubstantially facing the segments 51.

Segments 52, whose major length extends transversely of the belts 9, maybe provided at the extremities of the devices for confining the cushions12.

As may be seen from FIGS 16 and 16a, the lateral extensions 48 of thedevices for confining the cushions 12 and 16 may cooperate with segments27 mounted in grooves formed on the lateral faces of the pulleys.

Because of the absence of jaw clutches, the space requirement of thedevice is that of a conventional gear box (smaller in width than aconventional gear box).

The transmission device according to the invention also has theadvantage of not introducing axial load on the shafts.

It goes without saying that the embodiments described are only examplesand that it would be possible to modify them, particularly bysubstitution of equivalent techniques, without departing for this reasonfrom the scope of the invention.

I claim:

1. Device for transmission of a rotary motion by means of belts,comprising on the one hand several transmission assemblies of which eachcomprises a driving pulley, at least one driven pulley and a belt whichis adapted to transmit a driving force from the said driving pulley tothe said driven pulley and on the other hand means of selectionincluding fluid cushion established facing at least a part of thecontact surfaces between pulleys and belts, to apply selectively eachbelt to its respective pulleys for transmitting a said drive effort.

2. Transmission device according to claim 1, in which one of the pulleysof each transmission assembly is connected to a single shaft, the otherpulley of each assembly being able to be connected to several shafts, itbeing possible for the transmission ratios of the said transmissionassemblies to be different.

3. Transmission device according to claim I, able to be used as a speedchange box for automobile vehicles, in which each transmission assemblycorresponds to a unique and different transmission ratio, a singleassembly being engaged.

4. Transmission device according to claim 2, able to be used as a speedchange box for automobile vehicles, in which each transmission assemblycorresponds to a unique and different transmission ratio, a singleassembly being engaged.

5. Transmission device according to claim 1, in which different drivepulleys are all mounted on a rotationally driven drive shaft and inwhich the different driven pulleys are mounted on a parallel drivenshaft, and als in which the said means of selection comprise achangeovervalve fed by a fluid under pressure and connected to conduits whichconduct the fluid towards each of the belts, the pressure of the fluidbeing thus directed at will under the control of the changeover valveonto the belt of the chosen transmission assembly, applying it againstits pulleys.

6. Transmission device serving as a speed change box for an automobilevehicle, according to claim 1, in which the difi'erent drive pulleys areall mounted on a rotationally driven drive shaft and in which thedifferent driven pulleys are mounted on a parallel driven shaft, andalso in which a toothed wheel is mounted on each of the said shafts,these toothed wheels being in mesh, one of the toothed wheels beingmounted fixedly on its shaft and the other being provided with means ofrendering it integral with the shaft, able to be actuated by selectionof thesaid oil pressure under the control of the said valve, to obtainreverse motion.

7. Transmission device according to claim 1, in which the lattercomprises means for applying a counterpressure of fluid in thetransmission assemblies which are not to function, to detach positivelythe belt from its pulleys.

8. Transmission device according to claim 1, in which the lattercomprises means for applying a counterpressure of fluid in thetransmission assemblies which are not to function, to positively detachthe belt from its pulleys, the said fluid being a gas under pressure.

9. Transmission device according to claim 1, in which the lattercomprises means for applying a counterpressure of fluid in thetransmission assemblies which are not to function, to detach positivelythe belt from its pulleys, the said fluid being constituted by oil fromthe housing of an automobile vehicle.

10. Transmission device for transmission of a rotary motion by means ofbelts, comprising on the one hand several transmission assemblies ofwhich each comprises a drive pulley, a driven pulley and a belt which isadapted to transmit a driving force from the said driving pulley to thesaid driven pulley and on the other hand selection means inlcudingcushions of fluid established facing at least a part of the surfaces ofcontact between pulleys and belts, to apply selectively each belt ontoits respective pulleys to transmit a said driving force, and a series ofradial passages formed in each pulley connecting to an axial passagethrough which another fluid can be supplied to apply a counterpressurefor detachment of the belt.

11. Transmission device for transmission of a rotary motion by means ofbelts, comprising on the one hand several transmission assemblies ofwhich each comprises a driving pulley, a driven pulley and a belt whichis adapted to transmit a driving force from the said driving pulley tothe said driven pulley and on the other hand selection means includingcushions of fluid established facing at least a part of the contactsurfaces between pulleys and belts, to apply selectively eac belt ontoits respective pulleys to transmit a said driving force, and a series ofradial passages formed in each pulley connecting to an axial passagethrough which another fluid can be supplied to apply a counterpressurefor detachment of the belt, this other fluid being oil serving to applya belt for the transmission of a driving force.

12. Transmission device according to claim 1, in which a saidtransmission assembly comprises a tensioner pressing on the belt totension it under the effect of a pressure of fluid.

13. Transmission device according to claim 1, in which a saidtransmission assembly comprises a tensioner pressing on the belt totension it under the effect of a pressure of fluid, the fluid acting onthe tensioner being constituted by oil under a pressure less than thatof the oil serving to apply a belt for the transmission of forces.

14. Transmission device according to claim 1, in which a saidtransmission assembly comprises, between the belts and the side opposedto that of the application of the belt on the pulley, an equilibratingchamber for the thrust on the shaft.

15. Transmission device according to claim 1, in which the cushions offluid under pressure are adapted to apply the belt substantially on halfof the circumference of the pulley.

16. Transmission device according to Claim 1, in which cushions of fluidunder pressure are adapted to apply the belt onto a small part, lessthan a half, of the circumference of the pulley.

17. Transmission device according to claim 1, in

which the cushions of fluid under pressure are adapted to apply the beltonto about a sixth of the circumference of the pulley.

18. Transmission device according to claim 1, in which a chamberprovided with perforations surrounds the pulley and in which means areprovided for supplying the said fluid into this chamber, such that thecushions of fluid under pressure apply the belt at several points of thecircumference of the pulley,

19. Transmission device according to claim 1, in which a chamberprovided with perforations surrounds the pulley and in which means areprovided for supplying the said fluid into this chamber, such that thecushions of fluid under pressure apply the belt at several points of thecircumference of the pulley, separating ribs being provided between thechamber and the belt, between the said perforations.

20. Transmission device according to claim 1, in which a saidtransmission assembly comprises a tensioner pressing on the belt totension it under the effect of a pressure of fluid, the said tensionerbeing provided with means for recovering surplus oil.

21. Transmission device according to claim 1, in which the pulleys areprovided with serrations on their surface cooperating with the belt in amanner to produce a better coefficient of driving of the said belt onthe said pulleys.

22. Transmission device according to claim 1, in which the pulleys areprovided with serrations on their surface cooperating with the belt in amanner to produce a better coefficient of driving of the said belt onthe said pulleys, the belt being deformed elastically by the pressure ofprojections constituting pseudo-teeth which cooperate with the hollowsof the pulleys.

23. Transmission device according to claim 1, in which the lateralsurfaces of the pulleys are provided with grooves cooperating withscraper elements to reduce the losses of liquid.

24. Transmission device according to claim 1, in which a saidtransmission assembly comprises a tensioner pressing on the belt totension it under the effect of a pressure of liquid, the tensioner beingactuated by a jack acting under the effect of oil under high pressure onone face and low pressure on the other, the whole in a manner to set thetensioner in action only when then the corresponding transmissionassembly is in service.

25. Transmission device according to claim 1, in which the beltconnecting the pulleys of one transmission assembly is crossed in amanner to reverse the sense of rotation of the said pulleys, the saidtransmission assembly being able to constitute the reverse drive of aspeed change box.

I III II II i

1. Device for transmission of a rotary motion by means of belts,comprising on the one hand several transmission assemblies of which eachcomprises a driving pulley, at least one driven pulley and a belt whichis adapted to transmit a driving force from the said driving pulley tothe said driven pulley and on the other hand means of selectionincluding fluid cushion established facing at least a part of thecontact surfaces between pulleys and belts, to apply selectively eachbelt to its respective pulleys for transmitting a said drive effort. 2.Transmission device according to claim 1, in which one of the pulleys ofeach transmission assembly is connected to a single shaft, the otherpulley of each assembly being able to be connected to several shafts, itbeing possible for the transmission ratios of the said transmissionassemblies to be different.
 3. Transmission device according to claim 1,able to be used as a speed change box for automobile vehicles, in whicheach transmission assembly corresponds to a unique and differenttransmission ratio, a single assembly being engaged.
 4. Transmissiondevice according to claim 2, able to be used as a speed change box forautomobile vehicles, in which each transmission assembly corresponds toa unique and different transmission ratio, a single assembly beingengaged.
 5. Transmission device according to claim 1, in which differentdrive pulleys are all mounted on a rotationally driven drive shaft andin which the different driven pulleys are mounted on a parallel drivenshaft, and als in which the said means of selection comprise achangeover valve fed by a fluid under pressure and connected to conduitswhich conduct the fluid towards each of the belts, the pressure of thefluid being thus directed at will under the control of the changeovervalve onto the belt of the chosen transmission assembly, applying itagainst its pulleys.
 6. Transmission device serving as a speed changebox for an automobile vehicle, according to claim 1, in whicH thedifferent drive pulleys are all mounted on a rotationally driven driveshaft and in which the different driven pulleys are mounted on aparallel driven shaft, and also in which a toothed wheel is mounted oneach of the said shafts, these toothed wheels being in mesh, one of thetoothed wheels being mounted fixedly on its shaft and the other beingprovided with means of rendering it integral with the shaft, able to beactuated by selection of the said oil pressure under the control of thesaid valve, to obtain reverse motion.
 7. Transmission device accordingto claim 1, in which the latter comprises means for applying acounter-pressure of fluid in the transmission assemblies which are notto function, to detach positively the belt from its pulleys. 8.Transmission device according to claim 1, in which the latter comprisesmeans for applying a counter-pressure of fluid in the transmissionassemblies which are not to function, to positively detach the belt fromits pulleys, the said fluid being a gas under pressure.
 9. Transmissiondevice according to claim 1, in which the latter comprises means forapplying a counter-pressure of fluid in the transmission assemblieswhich are not to function, to detach positively the belt from itspulleys, the said fluid being constituted by oil from the housing of anautomobile vehicle.
 10. Transmission device for transmission of a rotarymotion by means of belts, comprising on the one hand severaltransmission assemblies of which each comprises a drive pulley, a drivenpulley and a belt which is adapted to transmit a driving force from thesaid driving pulley to the said driven pulley and on the other handselection means inlcuding cushions of fluid established facing at leasta part of the surfaces of contact between pulleys and belts, to applyselectively each belt onto its respective pulleys to transmit a saiddriving force, and a series of radial passages formed in each pulleyconnecting to an axial passage through which another fluid can besupplied to apply a counter-pressure for detachment of the belt. 11.Transmission device for transmission of a rotary motion by means ofbelts, comprising on the one hand several transmission assemblies ofwhich each comprises a driving pulley, a driven pulley and a belt whichis adapted to transmit a driving force from the said driving pulley tothe said driven pulley and on the other hand selection means includingcushions of fluid established facing at least a part of the contactsurfaces between pulleys and belts, to apply selectively eac belt ontoits respective pulleys to transmit a said driving force, and a series ofradial passages formed in each pulley connecting to an axial passagethrough which another fluid can be supplied to apply a counter-pressurefor detachment of the belt, this other fluid being oil serving to applya belt for the transmission of a driving force.
 12. Transmission deviceaccording to claim 1, in which a said transmission assembly comprises atensioner pressing on the belt to tension it under the effect of apressure of fluid.
 13. Transmission device according to claim 1, inwhich a said transmission assembly comprises a tensioner pressing on thebelt to tension it under the effect of a pressure of fluid, the fluidacting on the tensioner being constituted by oil under a pressure lessthan that of the oil serving to apply a belt for the transmission offorces.
 14. Transmission device according to claim 1, in which a saidtransmission assembly comprises, between the belts and the side opposedto that of the application of the belt on the pulley, an equilibratingchamber for the thrust on the shaft.
 15. Transmission device accordingto claim 1, in which the cushions of fluid under pressure are adapted toapply the belt substantially on half of the circumference of the pulley.16. Transmission device according to Claim 1, in which cushions of fluidunder pressure are adapted to apply the belt onto a small part, lessthan a half, of the circuMference of the pulley.
 17. Transmission deviceaccording to claim 1, in which the cushions of fluid under pressure areadapted to apply the belt onto about a sixth of the circumference of thepulley.
 18. Transmission device according to claim 1, in which a chamberprovided with perforations surrounds the pulley and in which means areprovided for supplying the said fluid into this chamber, such that thecushions of fluid under pressure apply the belt at several points of thecircumference of the pulley,
 19. Transmission device according to claim1, in which a chamber provided with perforations surrounds the pulleyand in which means are provided for supplying the said fluid into thischamber, such that the cushions of fluid under pressure apply the beltat several points of the circumference of the pulley, separating ribsbeing provided between the chamber and the belt, between the saidperforations.
 20. Transmission device according to claim 1, in which asaid transmission assembly comprises a tensioner pressing on the belt totension it under the effect of a pressure of fluid, the said tensionerbeing provided with means for recovering surplus oil.
 21. Transmissiondevice according to claim 1, in which the pulleys are provided withserrations on their surface cooperating with the belt in a manner toproduce a better coefficient of driving of the said belt on the saidpulleys.
 22. Transmission device according to claim 1, in which thepulleys are provided with serrations on their surface cooperating withthe belt in a manner to produce a better coefficient of driving of thesaid belt on the said pulleys, the belt being deformed elastically bythe pressure of projections constituting ''''pseudo-teeth'''' whichcooperate with the hollows of the pulleys.
 23. Transmission deviceaccording to claim 1, in which the lateral surfaces of the pulleys areprovided with grooves cooperating with scraper elements to reduce thelosses of liquid.
 24. Transmission device according to claim 1, in whicha said transmission assembly comprises a tensioner pressing on the beltto tension it under the effect of a pressure of liquid, the tensionerbeing actuated by a jack acting under the effect of oil under highpressure on one face and low pressure on the other, the whole in amanner to set the tensioner in action only when then the correspondingtransmission assembly is in service.
 25. Transmission device accordingto claim 1, in which the belt connecting the pulleys of one transmissionassembly is crossed in a manner to reverse the sense of rotation of thesaid pulleys, the said transmission assembly being able to constitutethe reverse drive of a speed change box.